Syrian Civil Defense White Helmets, which has been authenticated based on its contents and other AP reporting, shows Civil Defense workers and Syrian citizens gathering after an airstrike hit a market in Maaret al-Numan in southern Idlib, Syria. AP

Turkish forces on Sunday shelled areas along its border with Syria's northwestern province, an area dominated by al-Qaida-linked militants, as Turkey's president says an operation in the area to enforce a "de-escalation" zone was underway "without problems."

Speaking Sunday, President Recep Tayyip Erdogan said the de-escalation zones would be applied in Idlib with "Russia outside, Turkey inside" with Syrian opposition fighters it backs.

"The process, which began with a step yesterday and started to be applied this morning, is continuing as you know and that effort is continuing in a calm way without problems" Erdogan said, speaking in the western province of Afyonkarahisar at the closing ceremony of his ruling party's conference.

The tension came a day after Turkey's president announced that his country has launched a "serious" operation in Syria's northwestern Idlib province with Turkey-backed Syrian opposition forces, following international efforts for de-escalation in the war-torn country.

Sejari said the operation aims to deploy Turkish-backed opposition fighters in the province currently dominated by al-Qaida-linked militants.

"So far our forces have not entered Idlib," Sejari said in an exchange of messages with The Associated Press.

The Britain-based Syrian Observatory for Human Rights said Turkish shells fell near a displaced people's camp along the border, causing a panic but no casualties. The Observatory said the shelling was followed by brief clashes and the lobbing of missiles as tension continued. The Observatory also said al-Qaida-linked militants have deployed new fighters to the area where the brief clashes occurred, in Kafr Lusin village, along the border.

The Observatory and another activist-operated news service, Thiqa, meanwhile reported that what appeared to be Turkish troops have entered Syria in a number of vehicles to deploy at an area between Idlib and Aleppo province. The reports say Turkish forces were escorted by al-Qaida-linked militants to Darat al-Ezzah area, which is only miles from Afrin, a Kurdish dominated enclave in western Syria. A Kurdish militiaman in Afrin confirmed that four Turkish vehicles were deployed in the area. He spoke on condition of anonymity because he was not authorized to speak to reporters.

There was no immediate Turkish comment on the reports. It was not immediately clear why or how there was an escort by al-Qaida-linked militants.

Erdogan said Sunday that Turkey would not allow a "terror corridor" by the Kurdish militia aiming to link its territories from eastern Syria to the Mediterranean.

He was referring to the U.S.-backed Syrian Kurdish militants that Turkey considers terrorists. The official Turkish news agency Anadolu said Saturday the new deployment would serve as a "wall" between Kurdish-controlled Afrin in northwestern Aleppo and Idlib province.

The plan to enforce a de-escalation zone in Idlib involves deploying Turkish special forces and observation points, according to Sejari, from the Turkish-backed Al-Mutasim Brigades. He said the plan is to also foil "foreign projects" that aim to occupy the north of Syria under the pretext of fighting terrorism, in an apparent reference to the U.S.-backed Kurdish forces.

Last year, the Turkish army launched a cross-border operation with Syrian opposition fighters to clear an area along its border of the Islamic State group and prevent the dominant Kurdish group from forming a contiguous entity from northeast to northwest Syria. There are no known plans by the Kurdish forces to take on al-Qaida-linked militants in Idlib.

Also, Turkish Foreign Minister Mevlut Cavusoglu told reporters late Saturday that Turkish observers would deploy in safe areas with no risk. He also said that Russian and Iranian observers would also be deployed in some areas, without providing further details.

Deploying Russian and Iranian observers could potentially be a controversial issue, considering that the Syrian opposition, backed by Turkey, views the two countries as enemies because of their support for the Syrian government.

Also Sunday, activists and residents of Maaret al-Numan in southern Idlib said an airstrike in the town's market killed at least eight people. Abdul-Rahim Almumar, a town resident, said it struck at a busy car park near a market, causing major destruction and a high death toll. The strike also caused a fire in an area store.

Almumar said at least 10 were killed, including at least two children. The Observatory put the death toll at 11 saying it was likely to climb as search and rescue operations continued.